1. Field of the Invention
The present invention relates to an optical scanner having an MEMS (micro electro-mechanical system) structure in which a frequency is tunable, and more particularly, to an optical scanner in which a resonant frequency is tunable by using a tuning electrode.
2. Description of the Related Art
Microactuators are used as scanners to deflect a laser beam in projection TVs. U.S. Patent Publication Application No. 2003-39089 discloses an example of an MEMS type scanner.
In an optical scanner disclosed in U.S. Patent Publication Application No. 2003-39089, a stage seesaws with respect to a torsion spring supporting the stage as a center shaft. As the stage is seesawing, light incident on a flat reflection mirror formed on the stage is scanned. The optical scanner deflects the stage connected to a driving electrode by applying an electrostatic force between a driving comb electrode and a fixed comb electrode.
In the MEMS type scanner, when the stage is driven in a resonant frequency range, a driving angle of the stage increases and a driving voltage is lowered. However, when an MEMS structure is accurately manufactured, it is very difficult to manufacture an actuator having a predetermined natural frequency due to a deviation in process. Also, a change in the resonant frequency may occur according to a change of surrounding environment.
U.S. Pat. No. 6,535,325 discloses a method of controlling a resonant frequency of an MEMS type optical scanner. That is, after a plurality of tuning tabs are installed at an edge portion of a stage, the tab is removed by a laser trimming or mechanical force while a frequency is measured, so that the weight of a mirror body is reduced. Thus, by increasing the frequency, the optical scanner is driven at a resonant frequency.